Technical Field
The present invention relates to semiconductor devices and, more particularly, to forming hybrid metal interconnects with a bamboo grain microstructure for semiconductor devices.
Description of the Related Art
Existing semiconductor devices often employ interconnects and/or contacts formed from a single material in a single layer. However, as device dimensions continue to decrease due to evolving technology, high aspect ratios of narrow features in the device, such as patterned features including interconnects and/or contacts, tend to increase. In addition, small grain structure within the narrow features persists due to the increased aspect ratios, especially toward the bottom of such narrow features even after annealing processes. These small grain microstructures in interconnect lines may significantly reduce electromigration performance of the semiconductor device.
Reducing the initial depth of the narrow features to lower the aspect ratios may improve grain growth, but at the expense of increasing line resistance. For example, at linewidths significantly less than 100 nanometers, a larger aspect ratio may prevent a bamboo microstructure from forming in the lines. Assuming a fixed linewidth constraint, however, means that having a shorter line decreases the volume of copper and thus increases electrical resistance. In addition, barrier layers embedded in the interconnect lines may sacrifice resistivity of the device, and high temperature annealing processes may affect via chain yield.